Transparent heat exchanger

ABSTRACT

In one aspect, a transparent heat exchanger includes a first transparent substrate optically attached to a heat source, one or more fins to transfer heat from the heat source, the one or more fins comprising transparent material and further comprising one of a manifold coupled to the first transparent substrate or a facesheet coupled to the first transparent material.

BACKGROUND

Some electro-optical devices such as laser gain media, for example,generate a significant amount of heat that must be removed efficientlyto avoid damage to the electro-optical devices or reduce theirperformance. In order to cool the electro-optical devices, heatexchangers (sometimes called heatsinks) are sometimes used to transferthe heat away from the electro-optical devices. In some examples, theheat exchangers transfer the heat to a fluid in motion.

SUMMARY

In one aspect, a transparent heat exchanger includes a first transparentsubstrate optically attached to a heat source, one or more fins totransfer heat from the heat source, the one or more fins comprisingtransparent material and further comprising one of a manifold coupled tothe first transparent substrate or a facesheet coupled to the firsttransparent material.

In another aspect, an optical window includes a first transparentsubstrate and a second transparent substrate optically bounded to thefirst transparent substrate and comprising one or more fins.

In a further aspect, a method to fabricate a transparent heat exchangerincludes optically bonding a first transparent substrate to a heatsource; forming one or more fins to transfer heat from the heat source,and coupling the first transparent substrate to one of a manifold or afacesheet. The one or more fins includes transparent material.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example of a configuration oftransparent heat exchanger system.

FIG. 2 is a block diagram of another example of a configuration oftransparent heat exchanger system.

FIG. 3 is a cross-sectional diagram of an example of a transparent heatexchanger system.

FIG. 4 is a flowchart of an example of a process to fabricate thetransparent heat exchanger system of FIG. 2.

FIG. 5 is a cross-sectional diagram of another example of a transparentheat exchanger system.

FIG. 6 is a flowchart of an example of a process to fabricate thetransparent heat exchanger system of FIG. 5.

FIG. 7 is a cross-sectional diagram of a further example of atransparent heat exchanger system.

FIG. 8 is a flowchart of an example of a process to fabricate thetransparent heat exchanger system of FIG. 7.

FIG. 9 is a cross-sectional diagram of a still further example of atransparent heat exchanger system.

FIG. 10 is a flowchart of an example of a process to fabricate thetransparent heat exchanger system of FIG. 9

FIG. 11A to 11C are diagrams of examples of a transparent heat exchangerin an optical window.

FIG. 12 is a flowchart of an example of a process to fabricate thetransparent heat exchanger system of FIG. 12.

FIG. 13 is a flowchart of an example of a process to form an opticalbond.

FIG. 14 is a flowchart of another example of a process to form anoptical bond.

DETAILED DESCRIPTION

Described herein are transparent heat exchangers. In one example, atransparent heat exchanger may include a transparent substrate with oneor more fins. In another example, a transparent heat exchanger mayinclude more than one transparent substrate. In a further example, atransparent heat exchanger forming an optical window may includetransparent substrates with at least one substrate having one or morefins.

As used herein the term “transparent” refers to a material's ability toallow wavelengths of light (e.g., visible or infrared), or at leastwavelengths of light above or below a particular wavelength, to passthrough the material. As used herein transparent material includessemi-transparent material and fully transparent material.

As used herein, the term “transparent heat exchanger” may be usedinterchangeably with the term “transparent heatsink.”

Some energy sources generate both thermal energy (sensible heat) andlight energy (such as fluorescence, stray pump light, and/or signallight). With prior art (non-transparent heat exchangers), the lightenergy is converted into thermal energy at the interface between thesource and the heat exchanger. The aggregated thermal energy and thenewly converted light energy must conduct through the heat exchangeralong the same path and into the coolant on the same surfaces. Asdescribed herein, the transparent heat exchanger enables improvedthermal performance by separating the functions of removing waste heatgenerated in the source and waste heat generated by light energyemanating from the source. The light emanating from the source may beconverted into heat within the bulk coolant, on separate heat exchangersurfaces from those conducting the waste heat, and/or the light may passcompletely through the heat exchanger. All cases result in greater heatexchanger performance due to lower heat per unit area of the heatexchanger facesheet and lower heat per unit area at the heat exchangerinterface with the coolant.

FIG. 1 depicts one example of a transparent heat exchanger system 100.The transparent heat exchanger system 100 includes a transparent heatexchanger 102 that is attached to a heat source 108 and is configured toremove heat from the heat source. In this configuration the transparentheat exchanger 102 is attached to one side of the heat source.

FIG. 2 depicts a transparent heat exchanger system 100′ incross-section. The heat exchanger system 100′ includes the transparentheat exchanger 102′ that at least partially surrounds the heat source108 and is configured to remove heat from the heat source 108.

In one particular example, the heat source 108 is a laser system (e.g.,a laser amplifier). In another example, the heat source 108 is a mirror.In a further example, the heat source 108 is a lens.

As will be further described herein the transparent heat exchangers 102,102′ each include at least one transparent substrate and further includeat least one of fins formed from transparent material or fluid channelsfor jet impingement to transfer heat.

Referring to FIG. 3, a transparent heat exchanger system 300, in oneexample, includes a manifold 302, a first thermal optical interface 304,a transparent substrate 306, a second thermal optical interface 320 anda heat source 326 (e.g., a laser amplifier). The manifold 302 includesfluid channels (e.g., fluid channels 334) used for jet impingement of afluid (e.g., coolant) to provide cooling. In some examples herein, athermal optical interface may be an optical bond that is able totransmit light of a desired wavelength. In some examples herein, athermal optical interface may be a thin film of fluid. As used herein, athermal optical interface is an interface that passes both thermal andoptical energy thru the interface

The transparent substrate 306 includes etched troughs (e.g., fluidchannels 354 to carry coolant), which form raised features in thetransparent substrate 306 called fins (e.g., fins 344). The fins 344provide an increased heat transfer area. In one example, the transparentsubstrate 306 is one of indium phosphate, silicon, silicon carbide,fused silica, sapphire, diamond or any other suitable material orcombination of materials. In one example, a coefficient of thermalexpansion (CTE) of the transparent substrate 306 is about equal to theCTE of the heat source 326 (e.g., differing by no more than 10 parts permillion per degree Centigrade (ppm/° C.)).

In other examples, the manifold 334 may be along one or both ends of thetransparent substrate 306 instead, or the manifold 334 may partially orwholly surround the transparent substrate 306.

Referring to FIG. 4, a process 400 is one example of a process tofabricate the heat exchanger system 300. The fluid channels 334 areetched in the manifold 302 and fluid channels 354 are etched into thetransparent substrate 306 (402). Surfaces of transparent substrate 306and the manifold 302 are smoothed for optical bonding (406). Thetransparent substrate 306 is bonded to the manifold 302 with thermaloptical interface 304 to form a bonded assembly (412). The surfaces oftransparent substrate 306 and the heat source 326 are smoothed (422).The transparent substrate 306 is optically attached (i.e., forming athermal optical interface that passes thermal and optical energy throughthe interface) to the heat source 326 with thermal optical interface 324(426). It should be understood that both surfaces of transparentsubstrate 306 may be smoothed at the same step.

In one or more embodiments described herein, various techniques may beused to form a smooth surface. For example, chemical or mechanicalplanarization of a surface may be accomplished to produce a smoothsurface by polishing, etching, or a combination of the two. In someembodiments, the surface may be smoothed by exposing the surface to anabrasive and/or corrosive chemical in conjunction with a polishing padthat is in contact with the surface and is moved relative to thesurface. In some embodiments, the surfaces may be smoothed to a surfaceroughness of less than 25 Angstroms (e.g., between 10 to 25 Angstroms, 5to 10 Angstroms, less than 5 Angstroms).

In one or more embodiments described herein, a typical flatness foroptics (bonded or unbonded) may be 10% of the wavelength (referred to aslambda/10). In one particular example, for a 1 micrometer wavelength,the flatness of the optics is 100 nm.

Referring to FIG. 5, a heat exchanger system 500, in one example,includes a facesheet 502, a first thermal optical interface 504, atransparent substrate 506, a second thermal optical interface 520 and aheat source 526 (e.g., a laser amplifier).

The transparent substrate 506 includes etched troughs (e.g., fluidchannels 554 to carry coolant), which form raised features in thetransparent substrate 506 called fins (e.g., fins 544). The fins 544provide an increased heat transfer area. In one example, the transparentsubstrate 506 is one of indium phosphate, silicon, silicon carbide,fused silica, sapphire, diamond, germanium, zinc selenide, zinc sulfideor any other suitable material or combination of materials. In oneexample, a CTE of the transparent substrate 506 is about equal to theCTE of the heat source 526.

In other examples, the facesheet 502 may be along one or both ends ofthe transparent substrate 506 instead, or the facesheet 502 maypartially or wholly surround the transparent substrate 506.

Referring to FIG. 6, a process 600 is one example of a process tofabricate the heat exchanger system 500. The fluid channels 554 areetched into the transparent substrate 506 (602). Surfaces of transparentsubstrate 506 and the facesheet 502 are smoothed for optical bonding(606). The transparent substrate 506 is bonded to the facesheet 502 withthermal optical interface 504 to form a bonded assembly (612). Thesurfaces of transparent substrate 506 and the heat source 526 aresmoothed (622). The transparent substrate 506 is optically attached tothe heat source 526 with thermal optical interface 520 (626). In oneexample, it should be understood that both surfaces of transparentsubstrate 506 may be smoothed at the same time.

Referring to FIG. 7, a transparent heat exchanger system 700, in oneexample, includes a manifold 702, a first thermal optical interface 704,a first transparent substrate 706, a second thermal optical interface708, a second transparent substrate 712 (sometimes called a “transparentfacesheet substrate” in this configuration), a third thermal opticalinterface 718 and a heat source 722 (e.g., a laser amplifier). Themanifold 702 includes fluid channels (e.g., fluid channels 734) used forjet impingement of a fluid (e.g., coolant) to provide cooling.

The first transparent substrate 706 includes etched troughs (e.g., fluidchannels 754 to carry coolant), which form raised features in the firsttransparent substrate 706 called fins (e.g., fins 744). The fins 744provide an increased heat transfer area. In one example, the firsttransparent substrate 706 and the second transparent substrate 712 areeach one of indium phosphate, silicon, silicon carbide, fused silica,sapphire, diamond, or any other suitable material or combination ofmaterials. The first transparent material 706 and the second transparentmaterial 712 may be the same or different material. The coefficient ofthermal expansion (CTE) of the first transparent substrate 706, the CTEof the second transparent substrate and the CTE of the heat source 722are about equal (e.g., the CTEs of the first transparent substrate, thesecond transparent substrate and the heat source differ by no more than10 parts per million per degree Centigrade (ppm/° C.) from each other.In some examples, the second transparent substrate 712 may be configuredto include etched troughs. In some examples, the second transparentsubstrate 712 may be configured to include etched troughs instead of thefirst transparent substrate 706.

Referring to FIG. 8, a process 800 is one example of a process tofabricate the heat exchanger system 700. The fluid channels 734 areetched in the manifold 702 and fluid channels 754 are etched into thefirst transparent substrate 706 (802). Surfaces of the first transparentsubstrate 706 and the second transparent substrate 712 are smoothed foroptical bonding (808). The first transparent substrate 706 is opticallybonded to the second transparent substrate 712 with thermal opticalinterface 708 (810). Surfaces of the first transparent substrate 706 andthe manifold 702 are smoothed for optical bonding (816). The firsttransparent substrate 706 is bonded to the manifold 702 with thermaloptical interface 704 to form a bonded assembly (822). It should beunderstood that both surfaces of the first transparent substrate 706 maybe smoothed at the same step.

The surfaces of the second transparent substrate 712 and the heat source722 are smoothed (832). The second transparent substrate 712 isoptically attached to the heat source 722 with thermal optical interface718 (836). It should be understood that both surfaces of the secondtransparent substrate 712 may be smoothed at the same step.

Referring to FIG. 9, a transparent heat exchanger system 900, in oneexample, includes a manifold 902, a first thermal optical interface 906,a transparent substrate 912, a second thermal optical interface 922 anda heat source 926 (e.g., a laser amplifier). The manifold 902 includesetched troughs (e.g., fluid channels 954), which form features in themanifold 902 called fins (e.g., fins 944). The fins 944 provide anincreased heat transfer area.

In one example, the manifold 902 is a transparent material being one ofindium phosphate, silicon, silicon carbide, fused silica, sapphire,diamond, or any other suitable material or combination of materials. Inone example, the transparent substrate 912 is one of indium phosphate,silicon, silicon carbide, fused silica, sapphire, diamond, or any othersuitable material or combination of materials. In one example, a CTE ofthe transparent substrate 912 is about equal to the CTE of the heatsource 926.

In other examples, the manifold 902 may be along one or both ends of thetransparent substrate 912 instead, or the manifold 902 may partially orwholly surround the transparent substrate 912.

Referring to FIG. 10, a process 1000 is one example of a process tofabricate the heat exchanger system 900. The fluid channels 954 areetched in the manifold 902 (1002). Surfaces of transparent substrate 912and the manifold 902 are smoothed for optical bonding (1008). Thetransparent substrate 912 is optically bonded to the manifold 902 withthe first thermal optical interface 906 to form a bonded assembly(1016). The surfaces of transparent substrate 912 and the heat source926 are smoothed (1028). The transparent substrate 912 is opticallyattached to the heat source 926 with the second thermal opticalinterface 922 (1032). It should be understood that both surfaces of thetransparent substrate 912 may be smoothed at the same step.

Referring to FIG. 11A, an optical window 1100 is a transparent heatexchanger that includes a first transparent substrate 1102, a thermaloptical interface 1104 and a second transparent substrate 1106. Thesecond transparent substrate 1106 includes etched troughs (e.g., fluidchannels 1154), which form features in the second transparent substrate1106 called fins (e.g., fins 1144). In this configuration, light (e.g.,with visible or infrared wavelength 1150) generated by a source (notshown) passes through the window 1100. In one example, the firsttransparent substrate 1102 includes at least one of indium phosphate,silicon, silicon carbide, fused silica, sapphire, diamond, or any othersuitable material or combination of materials. In one example, thesecond transparent substrate 1106 includes at least one of indiumphosphate, silicon, silicon carbide, fused silica, sapphire, diamond, orany other suitable material or combination of materials. In someexamples, the first transparent substrate 1102 may be configured toinclude etched troughs. In some examples, the first transparentsubstrate 1102 may be configured to include etched troughs instead ofthe second transparent substrate 1106.

In some examples, a void, vacuum or air gap 1120 may separate the firsttransparent substrate 1102 from the second transparent substrate 1106 inan optical window 1100′ (FIG. 11B).

In some examples, thermal optical interfaces (e.g., thermal opticalinterface 1114 and thermal optical interface 1124) may be included onsides of an optical window 1100″ (FIG. 11C).

In another example, the optical windows 1100, 1100′ and 1100″ may beused to reject heat due to parasitic conversion of a portion of signalenergy into thermal energy within the window substrate. In yet anotherexample, the optical windows 1100, 1100′ and 1100″ may be used to cool awindow that had been heated by other sources, for example, fromaerodynamic friction.

Referring to FIG. 12, a process 1200 is an example of a process tofabricate the optical window 1100. The fluid channels 1154 are etchedinto the second transparent substrate 1106 (1202). Surfaces of the firstand second transparent substrates 1102, 1106 are smoothed (1208). Thefirst and second transparent substrates 1102, 1106 are optically bondedtogether by the bond 1104. The first and second transparent substrates1102, 1106 are polished (1218) and coated with an optical coating(1222).

Referring to FIG. 13, a process 1300 is one example to perform opticalbonding described herein in the process 400, 600, 800, 1000 and 1200.Process 1300 includes forming oxide surface on the substrates to bebonded (1302) and bonding the substrates to form a covalent bond (1306).

Referring to FIG. 14, a process 1400 is another example to performoptical bonding described herein in the process 400, 600, 800, 1000 and1200 herein. Process 1400 includes applying transparent solder tosubstrate surfaces (1402) and bonding the substrates to form atransparent solder bond (1406).

In one example, the heat sources described herein may be from high-powerlaser systems. The high-power laser systems could be used in a largenumber of military and commercial applications. The following examplesdo not limit this disclosure to any particular application.

The processes described herein are not limited to the specific examplesdescribed. For example, the processes 400, 600, 800, 1000, 1200, 1300and 1400 are not limited to the specific processing order of FIGS. 4, 6,8, 10 and 12 to 14, respectively. Rather, any of the processing blocksof FIGS. 4, 6, 8, 10 and 12 to 14 may be re-ordered, combined orremoved, performed in parallel or in serial, as necessary, to achievethe results set forth above.

Elements of different embodiments described herein may be combined toform other embodiments not specifically set forth above. Variouselements, which are described in the context of a single embodiment, mayalso be provided separately or in any suitable subcombination. Otherembodiments not specifically described herein are also within the scopeof the following claims.

What is claimed is:
 1. A transparent heat exchanger comprising: a firsttransparent substrate optically attached to a heat source; one or morefins to transfer heat from the heat source, the one or more finscomprising transparent material; and further comprising one of: amanifold coupled to the first transparent substrate or a facesheetcoupled to the first transparent material.
 2. The transparent heatexchanger of claim 1, wherein the manifold is optically bonded to thefirst transparent substrate.
 3. The transparent heat exchanger of claim2, wherein the first transparent substrate comprises the one or morefins.
 4. The transparent heat exchanger of claim 1, wherein the manifoldcomprises channels used to supply coolant to the one or more fins and toreturn coolant from the one or more fins.
 5. The transparent heatexchanger of claim 1, further comprising a second transparent substratecomprising the one or more fins.
 6. The transparent heat exchanger ofclaim 5, wherein the second substrate is optically bonded to the firstsubstrate.
 7. The transparent heat exchanger of claim 5, wherein thesecond substrate is optically bonded to the manifold.
 8. The transparentheat exchanger of claim 5, wherein the second transparent substratecomprises at least one of indium phosphate, silicon, silicon carbide,fused silica, sapphire, germanium, zinc selenide, zinc sulfide, diamondor any combination thereof.
 9. The transparent heat exchanger of claim1, wherein the first transparent substrate comprises at least one ofindium phosphate, silicon, silicon carbide, fused silica, sapphire,germanium, zinc selenide, zinc sulfide, diamond or any combinationthereof.
 10. The transparent heat exchanger of claim 1, wherein acoefficient of thermal expansion (CTE) of the first transparentsubstrate and the CTE of the heat source differ by no more than 10 partsper million per degree Centigrade.
 11. The transparent heat exchanger ofclaim 1, wherein the manifold is along one or both ends of thetransparent substrate.
 12. The transparent heat exchanger of claim 1,wherein the manifold is partially or wholly surround the transparentsubstrate.
 13. A optical window comprising: a first transparentsubstrate; and a second transparent substrate optically bounded to thefirst transparent substrate and comprising one or more fins.
 14. Thewindow of claim 13, wherein the window is configured to pass a lightsignal through the first transparent substrate to the second transparentsubstrate through the second transparent substrate.
 15. The opticalwindow of claim 13, wherein the first transparent substrate comprises atleast one of indium phosphate, silicon, silicon carbide, fused silica,sapphire or diamond.
 16. The optical window of claim 13, wherein thesecond transparent substrate comprises at least one of indium phosphate,silicon, silicon carbide, fused silica, sapphire or diamond.
 17. Theoptical window of claim 13, wherein the first transparent substrate andsecond transparent substrate create a heat exchanger assembly and sealthe one or more channels at edges defined by fins, whereinelectromagnetic radiation is passed through the optical window.
 18. Amethod to fabricate a transparent heat exchanger comprising: opticallybonding a first transparent substrate to a heat source; forming one ormore fins to transfer heat from the heat source, the one or more finscomprising transparent material; and coupling the first transparentsubstrate to one of a manifold or a facesheet.
 19. The method of claim18, wherein forming one or more fins comprises forming one or more finsin one of the first transparent substrate or a second substrate coupledto the heat source and the first substrate to transfer heat from the oneor more fins to a coolant in contact with the one or more fins.
 20. Amethod to cool a heat source, comprising: attaching a transparent heatexchanger to the heat source, wherein the transparent heat exchangercomprises: a first transparent substrate optically attached to the heatsource; one or more fins to transfer heat from the heat source to acoolant in contact with the one or more fins, the one or more finscomprising transparent material; and further comprising one of: amanifold coupled to the first transparent substrate or a facesheetcoupled to the first transparent material.